Powering Imp using VIN. Red-blinking light

This seems like a good spot for this:

I’m trying to power my imp through the VIN. I’m getting a red blinking light.

I’m using the Imp to turn a coffeemaker on & off. It works when powered by USB but not with VIN. Attached is a photo of the VIN setup that is giving me a red blinking light.

The coffeemaker’s circuit is active low. So when the buttons are pressed they are shorted to ground. [The voltage between the switch and the ground is 2.5V]

So, I’ve simulated a button press by connecting pin8 to the on/off switch and connecting the Imp’s GND to the ground I found on the coffeemaker’s circuit board. Then, in the imp planner, I’m making the pin temporarily pull the switch low to turn the machine on and off.

Next to the ground is a powered pin running at 5V. So, I soldered it to the VIN. It gets enough power to blink red non-stop.

BUT! If I manually press the on/off switch (and thus the heating element turns on) the IMP loses all power.

Could someone explain this to me and/or give me suggestions on how to successfully power the IMP off of the existing circuitry (no battery or additional power supply?

Thank you in advance!

Documentation says http://devwiki.electricimp.com/doku.php?id=april&s[]=vin:


This pad is connected to the input voltage being fed to the board - either the USB 5v supply or the reverse-voltage protected battery pads."

It is my understanding that VIN is an output, not an input. You would want to connect 5v and GND to the P+ & P- pads.

For reference, here is part of the April board. VIN comes from either the USB or P+P- pads depending on your jumper. It looks like there is actually a diode on the Battery pad line, so no current could flow.

Ah. I was thinking it stood for Voltage Input.

I thought the same thing (maybe it’s an output) and connected to the P+ and P- pads before posting… to no avail. I was rather mindless while doing it. I think I’ll try it again and take better notes on the matter.

I think that April and Amber need an onboard LiPo charging circuit. Lilly?

It does stand for Voltage Input… just think of it as… The voltage that I used for input, available as an output. Its very handy, you then have the 3V3 output from the DCDC as well as whatever you powered the board with to use with external modules.

Weird that the pads didnt work… was your jumper in the right spot?

The reason that’s not working is very likely because though the pin you’ve found is 5v, it has nowhere near enough current available to run an imp. If you measure the voltage with the imp connected, you’ll likely find it’s unstable and goes quite low. There’s no reason why a simple coffee maker circuit would need enough power to run a wifi chip, so they didn’t design their power supply to do so.

Note also that the power supply here is very unlikely to be isolated, so the imp ground could be live if your house or socket is miswired. There’s a reason these things are all sealed up inside a housing :slight_smile:

VIN is the right place to feed power, though.

@Hugo So, applying power at VIN is the same as applying power at the P+P- pads? Nothing in the circuit that would prevent it from powering the Imp?

The P+/P- pads have reverse voltage protection, and the power then goes through the input select jumper. The VIN pad is at the output of the input select jumper.

Powering using the VIN pad is just fine, as long as you have the polarity correct :slight_smile:

@jwehr, the drawing of the April board is excellent. Thank you for that. Was it in the documentation?

Also, I tried the P+P- pads and @Hugo nailed it - the voltage is very unstable; dropping very low and at a regular pace. [Basically, the red blinking light is the result of it turning on and off.]

Also, @Hugo. Good to know that I should power the imp through the VIN in this instance.

So all this being said, what are some options for powering the imp neatly? Is a LiPo charging unit in order as @jwehr mentioned?

My goal is that the user (i.e. myself) never has to mess with the imp beyond blink up. So manually charging, or replacing batteries is something I want to avoid.

My last resort is to use a USB wall charger. But naturally this isn’t preferred as it means my coffeemaker would take up two plugs.


Ahh good. I was mostly correct then. I wasn’t sure if current could flow both ways through the DMG230 MOSFET.

I second that… Hugo, thanks for the reminders about hacking kitchen appliances.

That schematic is from Eagle files. You can download a free version, and Sparkfun has the Eagle files available for the April v1.1

I have a lot of projects that I want to power with LiPo’s which is why I commented on it. The Amber board has a lot of free space, and unless there is an electrical reason not to, I would love to slide either one of Sparkfun or Adafruits open hardware LiPo charger designs onto it. If all goes well with my current Amber board run, that might be my next hardware project.

Really, the easiest way to make it all integrated is to try and fit a phone charger inside the coffee machine housing, connecting it to the AC input on one side and to the imp on the other. You don’t need a battery, and it’d be powered direct from the coffee machine’s AC lead.

When you do this, the ground connection between the imp and the control board of the coffee machine will tie imp ground to line neutral - this was floating, when it’s just powered by the charger brick). The connection needs to be made if you want to simulate a button press, and should be safe if you are going to seal everything up and not touch the imp.

The issues here are that you’re touching the AC wiring, and hence you need to be very careful (and never touch any of the wiring, low voltage or otherwise, when AC is connected).

Those little cube chargers are probably about as small as you can get… I wonder if the circuitry is available without the packaging.

The neatest way would be to leave it housed, dremel off most of the AC pins and then solder to them/insulate well…

@jwehr, good thought. I’m going to search for a USB charger without the shell. That would be excellent. Otherwise I would have to solder the prongs directly to the AC leads? Seems kind of precarious.

@hugo, I haven’t worked with AC current before [because of it’s hazards.] But, I can very easily see the AC leads and imagine how to go about it safely. Despite this, is there anything else I should know? I think I’ll take a photo of my setup before powering it up and share it here… to see if anything jumps out as idiotic.

Hugo’s idea is a good one. Leave the housing on the cubes… probably isn’t much room inside anyway. probably have to sand the plugs down to copper to solder to them? Emory paper?

Ive been wanting to impify one of my electrical outlets. PowerTails would work fine too, but it would be cool to have everything in the box.

Here is a digikey search:

Apple: http://store.apple.com/us/product/MD810LL/A/apple-5w-usb-power-adapter?fnode=3c
Emerson: http://www.digikey.com/product-detail/en/DCH5-050US/454-1499-ND/2643404

Thanks @jwehr, I’m looking into a good way to connect the prongs to the AC leads. What do you mean by sand down to the copper? I suppose they’re nickel-plated to stop them from corroding? And you want to sand them down because solder won’t bond to that coating. Am I understanding you correctly?

…If so, I got a Dremel that could see some action here. :slight_smile:

While I’m looking into this, I found a less than ideal but decent solution. I found a third party USB wall plug, a compact wall plug splitter and a sweet teal USB cord in the junk drawer! See the photos.

Yep, thats what I mean about the the coating, I don’t think you can solder to it. The dremel should work nicely if you want to connect to the AC leads inside the coffee maker. I think that white adapters like you have there are the smallest I have found.

You could carefully dremel back the plastic around the leads… I would think youll find solder joints just inside, or grind off the coating until you can get a good solder joint. I think I would go with the latter. Use a chunk of old extension cord and connect the adapter to wherever you can solder to the AC power coming into the pot.

I should probably Imp my pot one of these days. Too many projects, too little time.

I could Imp my kegerator…:slight_smile:

Here is a possibility.
Not sure where the 63% efficiency ranks it though.